1. Field of the Invention
The present invention relates to electrical cables of the type used in undersea applications such as for electric submersible pumps and the like.
2. Description of the Related Art
Electrical cables are used to interconnect electric motors to submersible pumps or other equipment in oil and gas wells. These cables ordinarily consist of three solid or stranded electrical conductors that are combined into a single cable.
Electrical cables for submersible pumps and the like contain copper conductive cables that must be protected from the extremely corrosive effects of the well fluids that surround the cable. Typical current designs for submersible pump cables use outer metal armor that is wrapped around a rubber jacket. The jacket surrounds a number of insulated conductors. The armor protects the conductors against impacts and abrasion. Lead sheaths around the insulated conductors are employed with some cables to provide protection against hydrogen sulfide and other corrosive chemicals. This arrangement is sturdy and provides significant protection against external physical hazards. In some of these arrangements, the lead sheaths are applied to the insulated conductors by wrapping lead strips helically around the insulated conductors. In others, the lead sheaths are extruded around the insulated conductors.
A problem inherent to armored cables is that the outer steel armor corrodes over time. Corrosion may occur when stored on the surface or it may occur in a well due to chemical attack. Such corrosion costs the industry millions of dollars annually. The armor can corrode to the point that its integrity is lost. When this occurs, gases trapped within the cable while in a well may decompress while pulling the cable from the well. This may rupture the cable causing the cable to fail electrically. In addition, corroded away portions of the external armor will tend to foul or contaminate the wellbore.
A related consideration for submersible pump cables is the cost and difficulty of manufacture of the cable. Some cable designs that provide sufficient protection against both corrosion and physical hazards are known, however, they are costly and difficult to manufacture. U.S. Pat. No. 3,809,802 issued to Pearson, for example, describes a round submersible pump cable in which the three conductors in the cable are twisted into a bundle in a braid-like fashion. Lead shielding is provided around each of the conductors. In order to manufacture this type of cable, the lead shields must be first encased with an extruded plasticized nylon or other abrasion resistant plastic. The plastic used must have particular properties of pliability, abrasion resistance, and the ability to withstand high temperatures. In addition, the plastic must be compatible with the rubber jacket that surrounds it and, as a result, the number of materials that are suitable is somewhat limited. Further, extruding the abrasion resistant material over the lead shields adds an extra manufacturing operation that must be performed in making the cable and can be costly.
The present invention provides an improved cable and cable sheathing arrangement that affords protection for the conductive elements against corrosion, chemical and physical hazards.
In a first exemplary embodiment, a round cable is described that includes a plurality of copper conductors that are encased in a thermoplastic insulation. In an alternative exemplary embodiment described herein, a flat cable is described that includes a plurality of copper conductors that are individually encased in a thermoplastic insulation and disposed in a side-by-side relation to one another. In both cases, an extruded lead sheath surrounds the thermoplastic insulation. In the case of the rounds cable, the three lead sheathed conductors are cabled together. Finally, a thermoset or thermoplastic jacket encloses the lead sheaths of the conductors to provide a unitary cable. The jacket is in surrounding contact with each of the lead sheaths so that at least a majority of the outer circumference of the sheaths are contacted by the jacket. It is preferred that at least xc2xe of the outer circumference is in such surrounding contact with the jacket, and in the most preferred embodiment, the entire circumference of the sheaths are surrounded by and substantially contacted by the jacket. A cost effective cable is provided, and the need for an external metal armor is reduced or eliminated. Additionally, the cable provides substantial and adequate resistance to corrosion and physical hazards.